Fjrs.futa.edu.ng

FUTA Journal of Research in

Sciences ISSN: 2315 – 8239 (Print); E-ISSN: 2489 - 0413

FUTA Journal of Research in Sciences, Vol. 13 (2), October, 2017: 371-383

CHEMOSTRATIGRAPHY OF THE LIMESTONE IN FORMATION AT ITS HYPO-STRATOTYPE IN SAGAMU,

Peter S. Ola Department of Applied Geology The Federal University of Technology, Akure, Nigeria Correspondence: [email protected] ABSTRACT The limestone part of the Ewekoro Formation as exposed at a mining site in Sagamu was subjected to lithostratigraphic and geochemical studies. The study aims at a more detailed lithologic description including major elements determination of the limestone deposit at bed levels to better understand the richness of the rocks in terms of calcium content and its sedimentology. Detailed lithostratigraphy of the outcrop was carried out in the field; samples taken were studied using atomic absorption spectrometer (AAS) and gravity method. The samples were scanned using scanning electron microscope. The exposure consists of five beds of two groups of limestone: packstone (Beds, 2, 4 and 5) and wackstone (Beds 1 and 3). Three layers of motorable hardground separated the beds (one between bed 1 and 2, the second between bed 2 and 3 and the third between the limestone and the overlying shale). The richest bed in terms of CaO2 is Bed 3, which also have the lowest SiO2, reflecting the bed that was deposited in the deepest environment. Directly on top of the limestone is the Akinbo shale which consists of two shale facies – black and grey. Generally the limestones were deposited under varying environment of deposition and have been subjected to some varying environmental condition.

Keywords: Ewekoro Formation, limestone, beds, hardground, Calcium Oxide

INTRODUCTION thickness of 34 m at Ibeshe (Fayose and Assez, The Ewekoro Formation is one of the stratigraphic 1972). The Ewekoro Formation has its type units in the Nigerian part of the Dahomey Basin locality at the Ewekoro limestone quarry. There, it (Fig.1). It conformably overlies the Afowo consists of 10 to 12.5 m of thinly bedded Formation (old name – Formation). The glauconitic and sandy limestone at the base, which formation is not encountered offshore and in then becomes massive grey and fossiliferous in the coastal boreholes (Reyment, 1965; Fayose, 1970; middle and fine grained, marly and algal in the Billman, 1976, 1992). Where not encountered, it upper part (Dessauvagie, 1975: Adegoke, 1977). is replaced by the predominantly shaley Imo The top highly scoured layer consists of red, Formation which uncomformably overlies the dense, glauconitic, phosphatic and fossiliferous Afowo Formation (Fayose, op. cit.). Borehole limestone. The Ewekoro Formation is highly studies have revealed that Ewekoro Formation is fossiliferous. Adegoke (1977) identified more lens – shaped, thinning out and eventually than 220 mollusks and echinoderm species and disappear in all directions. It has a maximum

371

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 subspecies from the formation. It also contains abundant foraminifera, ostracodes and algae.

Figure. 1. Geological Map of southwestern Nigeria Showing the location of the Study Outcrop in Black dot

The age of Ewekoro Formation is limestone unit. Evidences in favour of a Paleocene controversial with prevailing two schools of age for the Ewekoro Formation appear to be quite thought. Reyment (1965), Adegoke (1969), and convincing and very well documented. It is Adegoke et al. (1970) proposed a Paleocene age possible, however, that part of the sequence on the basis of the occurrence in the strata of exposed at Ewekoro and also occurring in macrofossil and microfossil assemblages. The boreholes in southwestern Nigeria (especially the foraminiferal assemblage consists of by shales overlying the limestone i.e. Akinbo Globorotalia pseudobulloides, G. velascoensis, G. Formation) could be lowermost Eocene in age acita, Globigerina triloculinoides and G. (Odebode et al., 1996) linaperta. Reyment (1965) also listed a typical The Ewekoro Formation is exposed in Paleocene ostracode fauna retrieved from the several limestone’s quarries in southwestern formation. However, Fayose and Assez (1972) Nigeria (Ewekoro, Shagamu and Onigbedu); disagreed with the Paleocene age. They pointed Benin and Togo Republic where it is being used out that the presence of Globorotalia subbotinae for cement production. Investigation of the Morozova (a Lower Eocene index fossil) and other limestone as a source of raw materials for cement diagnostic Lower Eocene fossils (including production started in 1956 by Associated Portland Bolivina ottaensis and pseudohastigerian Cement Manufacturers, Limited. According to wilcoxensis) in the strata is significant and should Adegoke et al (1980) the formation is about 11 m not be overlooked. They therefore placed the thick, and consists of yellow and pale grey shelly Paleocene – Eocene boundary in southwestern limestone at its type locality in Ewekoro. Nigeria within some calcareous shale – limestone This study aims at a more detailed interbedded sequence below the massive shelly lithologic description of the beds of the formation

372

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 at a better exposed section in Sagamu. The major block –faulted giving rise to series of horst and element geochemical analysis of the limestone at graben (Bodashe Horst, Ilepaw Horst, Afowo beds level is carried out to understand the richness Graben, Ojo Platforms, Orimedu Graben and Ise of the rocks in terms of calcium content and clastic graben (Omatsola and Adegoke, 1981) that are influx that may serve as pollutant to the limestone, still active till date (Ola and Olabode, 2018). and the degree of alteration of the limestone. This Sediment accumulation in the basin varies in determination was carried out to ascertain if the thickness on the on-shore coaster section from studied rocks were subjected to alteration or not 100m to 1,400 m along strike and well over 2,000 and their usefulness for industrial purposes. m in the offshore part of the basin.

GEOLOGICAL SETTING Stratigraphy The Dahomey Basin is a one-sided source The stratigraphy of the Cretaceous and Tertiary asymmetry basin that occupies the intermediate formations in the Nigerian sector of the basin is crustal zone between thick continental crust and controversial. This is primarily because different thin oceanic crust. Evolution of the basin was in stratigraphic names have been given to the same response to the opening up of the Central and formation in different localities in the basin South Atlantic in the Middle Jurassic and that of (Billman, 1992; Coker 2002). This situation can the Cretaceous times. According to Omatsola and be partly blamed on the lack of good borehole Adegoke (1981), deposition was initiated in the coverage and adequate outcrops for detailed fault controlled structural depression on the stratigraphic studies. Earlier studies on the basin crystalline basement complex during early stratigraphy by Jones and Hockey (1964) Cretaceous. The subsidence led to the deposition recognized both Cretaceous and Tertiary of a very thick (over 1400m) sequence of sediments. Other subsequent workers recognized continental grits and pebbly sands over the entire three chronostratigraphic units: (i) pre-Lower basin, which covers parts of Southwestern Nigeria, Cretaceous folded sequence, (ii) Cretaceous the Benin Republic, Togo and Ghana (Lehner and sequence, and (iii) Tertiary sequence (Omatsola Ruiter, 1977). During the Santonian there was and Adegoke, 1981; Billman 1992). Figure 2 another episode of major tectonic activity in the summarizes the generalised stratigraphic column basin that was probably associated with the showing age, lithology, and sequence of the closure and folding of the Benue Basin. The formations and tectonic stage of basin basement rocks (granite gneiss and associated development in the Nigerian sector of the Benin pegmatite) as well as the uncomformably Basin (Ola and Olabode, 2017). overlying sediment in the basin were tilted and

373

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

Cretaceous Successions Formation lays uncomformably on the Afowo The Cretaceous stratigraphy as compiled from Formation (Bilman, 1992). outcrop and borehole records consists of Abeokuta The shales of the Akinbo Formation grade Group sub-divided into three informal formational into the overlying mudstones and claystones of the units, namely, Ise, Afowo, and Araromi (Omatsola Oshosun Formation. The presence of glauconites, and Adegoke, 1981). phosphates and abundant planktic foraminifera in the Oshosun Formation indicates deposition in a Tertiary Successions fairly deep marine environment, probably in the The oldest Tertiary sequence in the Dahomey bathyal zone. Overlying the Oshosun Formation, is Basin is the Ewekoro Formation, the focus of this the Formation, described by Jones and study. The Ewekoro Formation (where Hockey (1964) in shallow boreholes drilled at the encountered) is uncomformably overlain by the Akinside and areas. The Ilaro Formation predominantly shaley formation, which Ogbe consists of coarse, angular and poorly sorted sand (1972) named Akinbo Formation. Where the with considerable amount of clay layers and few Ewekoro Formation is missing, the Akinbo occurrence of shale. Capping all the formations is the often referred to as Coastal Plain Sands (Jones

374

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 and Hockey, 1964). It consists of yellow and Digestion and Analytical Determination of Major white, sometimes cross-bedded sand, pebbly beds Elements in the samples and clays with some sandy clay lenses. Its Five grams of the representative sample was thickness is unknown except in the Niger Delta weighed into crucible and digested with 10 mL where it measures about 2000 m (Merki, 1972). nitric acid. The mixture was warmed and filtered into 100 mL standard flask. The residue was METHODOLOGY further washed with distilled water and added to Data collection. the solution and make up to the mark for analysis For administrative purposes, the exposed of the metals. The residue was dried at 1050C, limestone deposits in Sagamu quarry is divided cooled and transferred into a weighed Teflon into three phases (, main and Sagamu) by beaker and then re-weighed. Then 10 mL the operating company (Plate 1). Each of the hydrofluoric acid was added, heated until dryness phases are also divided into three benches (lower, and then weighed to determine the silica content. middle and upper). Stratigraphically, five distinct The major elemental determination was carried out beds (Plate 2) could be identified at each of the to determine the following elements from where phases, which guided our sampling procedures. there oxides were calculated: Ca2+, Mg2+, Fe2+, Representative samples were taken in each bed Mn2+, Ni2+, Na+, K+ and Al3+ using Flame Atomic and within each of the phases. In all fifteen Absorption Spectrometery (FAAS); while classical samples were selected for study gravimetric method was used to determine the amount of Si in the samples .

Plate 1. Photography of each of the phases of the limestone deposit. The division is based on the operating company’s administrative purposes. Not taken to scale for reasons of distance

375

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

RESULT INTERPRETATION Fossils present include; pelecypod, cephalopod and gastropod. This bed is well cemented but with Lithostratigraphy and Mode of Occurrence of few vugs arranged in pockets within it. The vugs the Limestone and its Overlying Shale. are not connected and likely formed as a result of The limestone as exposed at the Sagamu quarry total decay of fossils occupying the space. varies laterally and vertically both in thickness and Towards the upper part of the bed, there is an textural features. Five distinct beds (Plate 2) could increase in the quantity of skeletal fragments and be identified at the Sagamu quarry. Each of the reduction in silica content. The grains are not well beds varies in thickness from 2.3 m to 4.5 m. rounded, medium sized and exhibit variable sizes. Beds1 and 2, 2 and 3 and 5 and the overlying shale There is a development of springs at the base of are separated by hardground. The hardground is a this bed. The thickness of the bed is generally less highly cemented layer of sandstone. They are than 3 m. A scanned slide of the section of the parallel to bedding planes and probably represent limestone bed reveals the occurrence of shell diagenetic precipitation resulting from basin fragments, micritic matrix and non-carbonate development pauses. The overlying shale deposit grains (quartz) (Plate 3). The matrix is of higher is the Akinbo Formation. percentage as shown on the scanned slides. Limestone The second bed exhibits gradational Geological Description of the Beds contact with the underlying one. The This is the first unit that is delineated in the lower distinguishing feature is the gradual change in bench and it is exposed in all the three phases. It colour from the bed below. The colour varies from varies in colour from dark grey to greyish white light grey to white with light brown patches. It and occasional light brown to milky white. It is contains abundant fossils. Fossils delineated are siliceous, micritc and contains abundant fossils. cephalopod and gastropod. The bed is less

376

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 indurated than the one below. The thickness of the micrite matrix (quartz) (Plate 3). The grains are of bed varies from 1.5 to 2.5 m. A scanned slide of large size with smaller matrix when compared the thin section prepared from the limestone with the lower bed. reveals the occurrence of shell fragments and

Bed 3 is separated from bed 2 by a very sharp, quantity of grains in the thin section. More grains highly indurated very thin layer that is less than 15 are present on one side of the thin section when cm thick of cemented limestone (hardground). The compared to the other. Sorting in the limestone most striking feature of this bed is the occurrence can be described as highly variable. Skeletal grains of very dark colour, which distinguishes the bed are not rounded, but fairly elongated and from others and allows it to be easily recognized moderatly sized. in the quarry. The thickness of the bed is generally The contact between bed 4 and bed 3 is less than 3 m and contains abundant fossils, shell also very sharp and highly indurated. This layer is fragments and probably detrital materials. A thin and is less than 12 cm in thickness. The scanned slide of the thin section prepared from the colour of the bed is predominantly light brown, limestone reveals the occurrence of shell containing few milky white spots. The thickness of fragments and micrite matrix (quartz) (Plate 3). A bed 4 is approximately 1.8 m and contains sharp transition can also be observed in the abundant fossils and shell fragments. Scanned thin

377

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 section of the limestone reveals occurrence of Distribution of major elements in the three phases abundant shell fragments and micrite matrix of the limestone gives an indication of the (quartz) (Plate 3). The sorting of the bed is fairly different chemical composition of the limestone poor. deposits encountered in Sagamu quarry (Tables 1, Bed 5 is the topmost limestone unit in 2 and 3). The ternary diagrams also confirm this Sagamu quarry. It is capped by hardground that (Fig. 3). Generally, the samples analyzed from all separates it from marine shale above. The the three phases of the quarry exhibit high Ca2+ thickness of the hardground is generally less than relative to the less mobile residual constituent of 15 cm. The colour of the bed is predominantly Al3+(Tables 1, 2 and 3). Similarly where the CaO white to milky white containing few light brown values are low the SiO2 are high. patches. The thickness of the bed is approximately 3.2 m. The bed contains abundant fossils and shell DISCUSSION fragments. Scanned thin section of the limestone Limestone Classification. reveals the occurrence of abundant shell fragments Adegoke (1969) revealed that the limestone of the and micrite matrix (Plate 3). Skeletal grains Ewekoro Formation is composed of three delineated include gastropods and others. The microfacies, which are sandy biomicrosparite, sorting of the bed is fairly highly variable shelly biomicrite and algal biosparite. At sagamu containing a mixture of small and large skeletal exposure of the limestone, five beds of different grains. facies were observed. The major element composition of each bed differ (Tables 1, 2 and 3). Shale The relationship between the micrite (matrix) and In a similar manner to the limestone, the shale is skeletal grains in Bed1 constituting the basal unit exposed at Ewekoro, the type locality of the shows that the bed contains abundant grains formation and the sagamu quarries. Two types of arranged in a matrix. The degree of grain shale facies occur in this area unlike its lateral roundness and size indicate poor sorting and equivalent in the type locality of Ewekoro possible short distance of transport. This type of Formation that has glauconitic shale facies. The limestone can be interpreted as product of low to two shale facies are the black (carbonaceous) and intermediate energy environments, because of the grey shales. Ironically too, only the grey shale occurrence of medium size grains in micrite facies is exposed at Ewekoro quarry. matrix. The limestone is similar to sparse The black shale is slippery, smooth and flaggy. biomicrite and wackstone of Folk (1962) and Most of the exposed sections are papery as a result Dunham (1962) respectively. Whereas, Bed 2 of well-developed fissility. Crystals of quartz contains abundant grains arranged in a low occur within the shale, growing from the run to fill quantity of matrix. The degree of grain roundness some cavities. Also, regular horizontal bands of and size indicate moderate sorting. This type of concretions are present. The thickness of this limestone can be interpreted as product of lithofacies is variable, essentially ranging from 3 intermediate to high energy environments, because m to 4.3 m overlying this carbonaceous shale is of the occurrence of fairly large size grains in the brownish grey shale of approximately 5 m micrite matrix. The depositional texture of the thick. Generally the shale is slightly variable in limestone can be described as packed biomicrite colour, slippery, smooth and papery. It contains and packstone (Folk, 1962; Dunham, 1962). quartz filling cavities and concretions also. Bed 3 can be interpreted as product of varying depositional environments, probably from low to Geochemistry moderate energy. The depositional texture of the

378

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

limestone can be described as a combination of energy. The high proportion of grains compared packed biomicrite and sparse biomicrite (Folk, with the lower proportion of micrite permits the 1962). It falls in the wackstone classification of classification of the limestone as packstone and Dunham (1962). The occurrence of abundant packed biomicrite of Dunham (1962) and Folk grains when compared to the matrix allows the (1962), respectively. classification of the limestone in Bed 4 as packstone and packed biomicrite of Dunham Chemostratigraphy. (1962) and (Folk, 1962) respectively. The texture Chemostratigraphy, or chemical stratigraphy, of the limestone contains a mixture of small and involves the characterization and correlation of large skeletal grains and these could be interpreted strata using major- and trace-element as product of varying energy of depositional geochemistry. Distribution of major elements in environments, probably from low to moderate Tables and ternary diagrams gives an indication of energy. The limestone of bed 5 contains a mixture the different chemical composition of the of small and large skeletal grains. With this the limestone deposits encountered in Sagamu quarry limestone formed under varying depositional (Tables 1, 2 and 3 and Fig. 3). environments, probably from low to moderate

Table 1 Concentration of oxides in percentages (%) Sagamu phase

Samples CaO MgO NiO Fe2O3 MnO Na2O K2O Al2O3 SiO2 LOI Total

S5 63.48 0.483 0.0076 0.4722 0.038 0.144 0.087 0.99 3.01 33.09 99.99

S4 64.11 0.589 0.0080 0.2794 0.029 0.160 0.099 0.98 2.81 31.14 100.00 S3 71.98 0.695 0.0076 0.3832 0.123 0.152 0.90 0.57 2.69 23.00 99.61

S2 77.51 1.373 0.0098 0.8852 0.015 0.179 0.134 0.55 2.29 17.01 99.89 S1 50.52 0.963 0.0086 0.8528 0.014 0.191 0.132 0.73 2.13 43.15 98.73

Average 65.52 0.332 0.0050 0.5746 0.044 0.165 0.108 0.76 2.59 29.48 99.64

Table 2 Geochemical analysis results for Lagos phase

Samples CaO MgO NiO Fe2O3 MnO Na2O K2O Al2O3 SiO2 LOI Total L2 59.58 0.523 0.0081 0.5085 0.024 0.161 0.112 0.10 1.36 36.43 99.80 L3 60.09 0.578 0.0083 0.6635 0.025 0.162 0.114 0.89 1.37 36.08 99.91 L4 62.84 1.284 0.0075 0.6118 0.026 0.182 0.115 0.90 1.42 31.89 99.27 L5 57.82 0.872 0.0077 0.7465 0.017 0.190 0.116 1.21 3.12 34.99 99.08 L6 7.87 0.921 0.0052 2.8560 0.006 0.191 0.453 12.56 57.01 18.05 99.92

Average 49.64 0.836 0.0074 1.0773 0.0196 0.177 0.182 3.332 12.86 31.49 99.60

379

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

Table 3 Geochemical Analysis results for Main phase

Samples CaO MgO NiO Fe2O3 MnO Na2O K2O Al2O3 SiO2 LOI Total M5 29.23 0.358 0.0060 0.6922 0.022 0.176 0.145 3.02 25.15 41.05 99.95 M4 48.53 0.563 0.0080 0.7056 0.025 0.188 0.127 2.08 9.85 37.94 99.99 M3 56.81 0.587 0.0079 0.0571 0.424 0.175 0.152 0.99 2.27 36.95 99.43 M2 53.02 0.772 0.0081 0.6183 0.011 0.183 0.110 0.94 2.10 42.00 99.76 M1 0.99 0.366 0.0029 0.1320 0.002 0.186 0.220 16.22 63.07 17.70 99.89 Average 37.72 0.531 0.0066 0.3351 0.097 0.182 0.151 4.65 20.49 35.13 99.78

Generally, the samples analyzed from all the three phases of the quarry exhibit high Ca2+ relative to the less mobile residual constituent of Al O Sagamu phase Al3+(Tables 1, 2 and 3). This implies that the 0 2 31 Lagos phase limestone is characterized by low chemical index Main phase of alteration (CIA) (Nesbitt and Young (1982). However, exceptional cases could be observed in 0.2 0.8 few samples from the Lagos and Main phases of the quarry with high Al3+ constituents with 0.4 0.6 Y s 2+ i A x corresponding low Ca . This is reflected in the x A is ternary plot as values not aligned in the right hand ZZ Y Ax Ax side of the triangle (Fig. 3). It also implies that 0.6 0.4 there are limestone beds within the quarry that is is have high values of CIA. These high values are interpreted as a consequence of surface weathering 0.8 0.2 processes or indicating severe alteration.

The percentage of SiO2 in the samples is not unconnected with clastic input of sediments 1 0 CaO SiO from the continents. Although this is generally low 2 0 0.2 0.4 0.6 0.8 1 in most of the samples, however there are samples XX Axis from the Lagos and Main phases of the quarry Ax with high percentages of SiO2 (Table 1, 2 and 3). is These samples correspond with samples characterized by high CIA. This indicate that Figure 3. Ternary plot for the percentages of during the formation of the limestone, there were major oxides in the Sagamu quarry. occasions whereby clastic input was greater than carbonate production and consequently possible Basin Development exposure to subaerial weathering. These combine There is an observed increase in the values of CaO processes may have resulted in high SiO2 and CIA from the lowest beds to bed 3 (S3, L4 and M3) in similar samples. before a decrease to the uppermost bed in the three phases. This is a reflection of the development of the basin of deposition of the limestone from continental to marine environment and back to a

380

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383 shallower environment. In other word, the lowest different environment of deposition. The beds are beds had influence of influx of continental classified as wackstone (Bed 1), packstone (Bed sediments. The black shale directly on top of bed 5 2), Wackstone (Bed 3), Packstone (Bed 4) and reflects the deepening of the basin after the packstone (Bed 5). Bed 3 is the richest in terms of deposition of the limestone. Black colourations in CaO2 and lowest in SiO2 content, which makes it shales are due to a very high content of unoxidized the best in cement production. The high organic matter (Prothero and Schwab, 1995). percentage of CaO, low SiO2 and Al2O3 in the Usually they are deep water sediments with poorly Sagamu phase of the quarry makes the limestone oxygenated (anoxic or dysoxic) conditions as a at this section of the quarry an ideal one for result of isolation of the bottom waters from cement production. However, the high CIA and effects of wind driven vertical advection of high SiO2 makes the limestone at Main and Lagos oxygen rich surface waters (Katz and Pratt, 1993). phases of the quarry an ideal hydrocarbon Non-stratification with other facies suggests reservoir, if the same conditions occur in the permanently deep and restricted basin without subsurface. fluctuations in oxygen content. A gradual change in the environment probably resulted into ACKNOWLEDGEMENT oxygenated conditions and deposition of the grey The chemical analysis was carried out under the shale. The quartz crystals present could be supervision of Prof. Albert Adebayo. Dr. S. O. interpreted as diagenetic structures filling cavities Olabode (while in the University of Glasgow) created by fossils. assisted in the Scanning of the samples. Both individuals are acknowledged with thanks. Hardground Carbonate hardgrounds were most commonly REFERENCES formed during calcite sea intervals in Earth Adegoke, O.S., (1969). Eocene statigraphy of history, which were times of rapid precipitation of southern Nigeria. Bull. Bur. Rech. Geol. Min. low-magnesium calcite and the dissolution of Mem 69: 23-48 skeletal aragonite (Palmer and Wilson, 2004). Adegoke, O.S., (1977). Stratigraphy and Carbonate hardgrounds are surfaces of paleontology of the Ewekoro Formation synsedimentarily cemented carbonate layers that (Paleocene) of southwestern Nigeria. Bull. have been exposed on the seafloor (Wilson and Amer. Paleont., 71: (295), 367. Palmer, 1992). Stratigraphers and sedimentologists Adegoke, O. S.,Ako, B. D., Petters, S.W., (1980). often use hardgrounds as marker horizons and as Stratigraphy of the Oshosun Formation in indicators of sedimentary hiatuses and flooding Southern Nigeria. J. Min. Geol. 17, (1), 97- events (Fürsich et al., 1981, 1992; Pope and Read, 106. 1997). In this study, samples of the hardground Adegoke, O.S., Dessauvagie, T.F.G., Kogbe, were not subjected to geochemical studies. C.A. and Ogbe, F.A., (1970). Type section, However, they serve as marker beds that probably Ewekoro Formation (Paleocene) of western formed during pauses in the development of the Nigeria. Biostratigraphy and microfacies. 4th basin. African Micr. Coll., Abidjan, 37-39. Billman, H.G., (1976), Offshore Statigraphy and CONCLUSIONS paleontology of the Dahomey The limestone deposit of the Ewekoro Formation embayment.Proc.7th Afr.Micropal.coll. Ile-Ife consists of five beds with varying major elemental Nig. (In press). compositions that suggests deposition under

381

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

Billman, H. G., (1992). Offshore Stratigraphy and AAPG Studies in Geology 37. Tulsa: Paleontology of Dahomey Embayment, West American Association of Petroleum Africa: Nigerian Association of Petroleum Geologists. Explorationists Bulletin, 72: 121-130. Lehner P, De Ruiter PAC 1977. Structural Coker, S.J. L., (2002). Field excursion guide to History of the Atlantic margin of Africa, tar sand outcrops in Benin Basin. NAPE American Association of Petroleum Mini-Conference, 32. Geologists Bulletin, 61: 961-981 Dessavagie, T.F.J., 1975. Explanatory note to the Merki, P.J., 1972. Structural geology of the geological map of Nigeria. Jour. Min. Geol. Cenozoic Niger Delta,African Geology, Univ. Nigeria, 9: (1,2), 3-28. of Press. 251-268. Dunham, R.J., 1962. Classification of carbonate Nesbitt, H.W., Young, Y.M., 1982. Early rocks according to their depositional texture, Paleozoic climates and platemotions inferred in W.E. Ham, eds, Classification of carbonate from major element chemistry of lutites. rocks – a symposium: Tulsa, OK. AAPG Nature 299: 715-717. Memoir 1: 108 – 121. Odebode, M.O., Ogunjobi, O. and Olowu, A.A. Fayose, E.A. and Assez, L.O., 1972. 1996. Paleogene Marine Condensed Sections Micropaleontological investigations of in the Onshore Eastern Dahomey basin, Ewekoro area, SW Nigeria. Micropal. 18/3: Southwest Nigeria. NAPE Bull. Book of 369-385. Abstracts, 1996, 34. Fayose, E.A. 1970. Stratigraphy and Paleontology Ogbe, F.G.A., 1972. Stratigraphy of strata of Afowo-1 well, Southwestern Nigeria. exposed in the Ewekoro quarry, western Journal Mining Geology 5: 1-99 Nigeria. Conf. proceeding on African Folk, R.L., 1962. Spectral subdivision of Geology, Ibadan, pp: 305-322. limestone types, in W.E. Ham, eds, Ola, P. S. and Olabode S. O. 2017. Tar sand Classification of carbonate rocks – a occurrence: Implications on hydrocarbon symposium: Tulsa, OK. AAPG Memoir 1: 62 exploration in the offshore Benin Basin, – 84. Petroleum Science and Technology, 35:6, Fürsich F.T., Kennedy, W.J., Palmer, T.J., 523-534, DOI: 1981. "Trace fossils at a regional 10.1080/10916466.2016.1265560 discontinuity surface: the Austin/Taylor Ola, P. S. and Olabode, S. O., 2018. Implications (Upper Cretaceous) contact in central Texas". of Horsts and Grabens on the Development of Journal of Paleontology. 55: 537–551. Canyons and Seismicity on the West Africa Fürsich, F.T., Oschmann, W., Singh, B., Jaitly, Coast. Journal of African Earth Sciences. Vol A.K., 1992. "Hardgrounds, reworked 140. 282 – 290. concretion levels and condensed horizons in Omatsola, M. E., Adegoke, O. S., 1981. Tectonic the Jurassic of western India: their evolution and Cretaceous Stratigraphy of the significance for basin analysis". Journal of the Dahomey Basin. Jour. Min. Geol. 8: 30-137. Geological Society of London. 149 (3): 313– Prothero, D.R. and Schwab, F., 1996. An 331. introduction to sedimentary rocks and Jones, H. A., Hockey, R.D., 1964. The geology of stratigraphy, Sedimentary Geology. W.H. part of Southwestern Nigeria. Geological Freeman and Company New York. 575. Survey of Nigeria. Bull. 31: 87. Reyment, R. A., 1965. Aspects of the Geology of Katz, D. L., and Pratt, L. M. (eds) 1993. Source Nigeria. Ibadan University Press. 145p. rocks in a sequence stratigraphic framework.

382

Ola., FUTA J. Res. Sci., Vol. 13 (2), October, 2017: 371 - 383

Palmer, T.J., Wilson, M.A., 2004. "Calcite Pope, M.C., Read, J.F., 1997. "High-resolution precipitation and dissolution of biogenic surface and subsurface sequence stratigraphy aragonite in shallow Ordovician calcite seas". of the Middle to Late Ordovician (late Lethaia. 37 (4): 417–427. Mohawkian-Cincinnatian) foreland basin Wilson, M.A., Palmer, T.J., 1992. "Hardgrounds rocks, Kentucky and Virginia". AAPG and hardground faunas". University of Wales, Bulletin. 81: 1866–1893. Aberystwyth, Institute of Earth Studies Publications. 9: 1–131.

383